Metal Gear Solid. Best game ever, even bought it off the playstation store for my PS3

I still like throwing that in and playing it once in a while. It really is one of those games that is timeless. It was also a breakthrough game back in the day. It launched the stealth genre and really pushed video games forward as a serious storytelling medium. Wasn't the first to do so but really was a major player. It basically raised the bar in video games.